1. Field of the Invention
The present invention relates to improvements of a driving apparatus and a light-amount regulating apparatus which are suitably usable in a shutter device and the like provided in an image pick-up apparatus such as a digital camera.
2. Related Background Art
Digital cameras for opto-electrically converting a field image and recording it as information of a still picture image in a recording medium by using a CCD and the like as a pick-up device have been more and more widely used. An example of the operation of exposure of those digital cameras will be discussed in the following.
The main power source is initially turned on prior to photographing to put the pick-up device in its operating condition, and the shutter blade is hence held at its open position capable of exposing the pick-up device. Accordingly, storing, discharging and transferring of electric charges are repeated by the pick-up device, and observation of the object field is made possible by the image monitor.
Upon pushing the release button, stop value and exposure time are determined corresponding to the output of the pick-up device at that time. Accordingly, when the diameter of the exposure aperture needs to be narrowed, the stop blade is driven to be set at a predetermined stop value. Instruction of start of storing electric charges is then sent to the pick-up device from which stored electric charges are discharged. At the same time the circuit for controlling the exposure time begins to operate upon reception of that start instruction as a trigger signal. After the lapse of a predetermined exposure time, the shutter blade is driven to its closed position for intercepting the exposure of the pick-up device. Upon intercepting the exposure of the pick-up device, the stored electric charges begin to be transferred. The picture image information is thus recorded in the recording medium through an image writing apparatus. Exposure of the pick-up device is blocked during the transfer of electric charges to prevent variation of electric charges due to undesired light during this transfer time.
FIG. 15 illustrates a small-sized stop apparatus or shutter apparatus. In the apparatus, a motor for driving the stop blade or the shutter blade is formed in a ring shape, and its inner portion is used as the optical path. Outer diameters of the stop apparatus and shutter apparatus can be hence reduced.
In FIG. 15, reference numeral 101 designates a cylindrical rotor whose outer surface portions are alternately magnetized into N and S magnetic poles. Reference numerals 102a and 102b designate coils which are respectively disposed along the axial direction of the rotor sandwiching the rotor. Reference numerals 103a and 103b designate stators formed of magnetic material. The stator 103a is magnetically excited by the coil 102a, and the stator 103b is magnetically excited by the coil 102b. Each of the stators 103a and 103b is comprised of an outer cylinder and an inner cylinder. The outer cylinder has an outer magnetic pole portion which extends in the axial direction in a planer form, and the outer magnetic pole portion is disposed in a position facing the outer surface of the rotor 101. The inner cylinder also has an inner magnetic pole portion which extends in the axial direction in a planer form, and the inner magnetic pole portion is disposed in a position facing the inner surface of the rotor 101. Reference numerals 104a and 104b designate auxiliary stators which are fixed to the inner cylinders of the stators 103a and 103b, respectively. Reference numeral 105 designates a coupling ring which is formed of non-magnetic material, and serves to couple the stators 103a and 103b to each other with a predetermined phase shift. Upon supplying electric power to the coils 102a and 102b, the outer magnetic pole portions of the stators 103a and 103b and the auxiliary stators 104a and 104b are excited, and the rotor 101 is rotated up to a predetermined position. Reference numeral 106 designates an output ring which is fixed to the inner surface of the rotor 101 and rotates together with the rotor 101. Reference numeral 107 designates a plate on which grooves for engaging with pins on the output ring 106 are formed. Those grooves regulate the rotational range of the output ring 106. Reference numerals 108a and 108b designate shutter blades which engage with the pins of the output ring 106, respectively, and whose opened condition is changed according to the rotational position of the rotor 101.
FIG. 16 illustrates another conventional structure in which the outer diameter of a motor is greatly decreased without making its inner portion hollow.
In FIG. 16, reference numeral 201 designates a cylindrical rotor 201 whose portions 201a and 201b are magnetized to the N and S magnetic poles, respectively. Reference numeral 201c designates an arm formed integrally with the rotor 201. A driving pin 201d extends from the arm 201c in the rotational axial direction of the rotor 201. Reference numeral 202 designates a coil disposed along the axial direction of the rotor 201. Reference numeral 203 designates a stator which is formed of soft magnetic material, and excited by the coil 202. The stator 203 has an outer magnetic pole portion 203a which faces the outer surface of the rotor 201, and an inner cylinder which is inserted into the rotor 201. Reference numeral 204 designates an auxiliary stator which is fixed to the inner cylinder of the stator 203, and faces the inner surface of the rotor 201. Upon supplying electric power to the coil 202, the outer magnetic pole portion 203a and the auxiliary stator 204 are excited, and the rotor 201 is rotated up to a predetermined position. Reference numerals 207 and 208 designate shutter blades, and reference numeral 205 designates a plate. The shutter blades 207 and 208 are respectively rotatable about hole portions 207a and 208a into which pins 205b and 205c of the plate 205 are inserted, respectively. The driving pin 201d slidably engages with elongate holes 207b and 208b. Reference numeral 206 designates a torsion spring which gives elastic force to the rotor 201 such that the driving pin 201d can be pushed against ends of the elongate 207b and 208b. When electric power is supplied to the coil 202 to rotate the driving pin 201d together with the rotor 201 against the elastic force of the torsion spring 206, the shutter blades 207 and 208 are rotated about the hole portions 207a and 208a, respectively. The aperture portion 205a of the plate 205 is thus opened or closed.
When no current is supplied to the coil 202, the elastic force of the torsion spring 206 brings the shutter blades 207 and 208 into the condition under which they close the aperture portion 205a. When current is supplied to the coil 202, the rotor 202 is rotated against the elastic force of the torsion spring 206. The aperture portion formed by the shutter blades 207 and 208 is enlarged as the magnitude of the current increases.
According to one aspect of the present invention, there is provided a driving apparatus which includes a rotatable ring-shaped rotor having magnet portions divided along a circumferential direction and differently magnetized; a first magnetic pole portion formed extending in a direction perpendicular to a rotational axis of the rotor, and facing a face of the magnet portion perpendicular to the rotational axis; and a second magnetic pole portion sandwiching the magnet portion between the second magnetic pole portion and the first magnetic pole portion, and facing another face of the magnet portion perpendicular to the rotational axis. In this driving apparatus, the condition of xe2x88x920.333X+0.7 greater than Y is satisfied where Y is a ratio of a central angle of each first magnetic pole portion relative to a central angle of each magnetized pole in the magnet portion, and X is a ratio of an outer circumferential length of each magnetized pole in the magnet portion relative to a thickness of the magnet portion in a direction of the rotational axis. In this structure, the rotor can be held at each of its two rotational positions due to cogging torque without supplying current to the coil.
According to another aspect of the present invention, there is provided a light-amount regulating apparatus which includes the above driving apparatus, a plate with an aperture portion, and a light-amount regulating member. In this structure, the amount of light passing through the aperture portion can be regulated by changing a direction of supplied current.
According to yet another aspect of the present invention, there is provided a lens driving apparatus which includes the above driving apparatus, a lens, and a lens holding member. In this structure, the lens can be driven by changing the condition of current supply, and the focal length of a light beam passing through the central portion of the rotor can be changed by changing a direction of supplied current.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.